Analyte sensors and methods

ABSTRACT

A sensor, and methods of making, for determining the concentration of an analyte, such as glucose, in a biological fluid such as blood or serum, using techniques such as coulometry, amperometry, and potentiometry. The sensor includes a working electrode and a counter electrode, and may include an insertion monitoring trace to determine correct positioning of the sensor in a connector. The sensor is calibration-adjusted, eliminating the need for a user to enter a calibration code or for the meter to read a calibration code.

FIELD OF THE INVENTION

This invention relates to analytical sensors for the detection ofanalytes in a sample, and methods of making and using the sensors.

BACKGROUND

Biosensors, also referred to as analytical sensors or merely sensors,are commonly used to determine the presence and concentration of abiological analyte in a sample. Such biosensors are used, for example,to monitor blood glucose levels in diabetic patients.

As sensors continue to be used, there continues to be an interest insensors that are easy to manufacture and easy for a patient to use.

SUMMARY

The present disclosure provides sensors and methods for the detectionand quantification of an analyte in a sample. The sensors are configuredto provide a clinically accurate analyte level reading, without the userhaving to enter a calibration code or the like that corresponds to thesensor. Embodiments of the sensor are provided, by the manufacturer ofthe sensors, with a configuration that provides a standardizedcalibration.

In general, certain embodiments of the invention include sensors foranalysis of an analyte in a sample, e.g., a small volume sample, by, forexample, coulometry, amperometry and/or potentiometry. The sensorsinclude at least a working electrode and a counter electrode, which maybe on the same substrate (e.g., co-planar) or may be on differentsubstrates (e.g., facing). The sensors also include a sample chamber tohold the sample in electrolytic contact with the working electrode. Asensor of the invention may utilize a non-leachable or diffusibleelectron transfer agent and/or a redox mediator. The sensors may beconfigured for side-filling, tip-filling, or top-filling. In addition,in some embodiments, the sensor may be part of an integrated sampleacquisition and analyte measurement device. An integrated sampleacquisition and analyte measurement device may include a sensor and askin piercing member, so that the device can be used to pierce the skinof a user to cause flow of a fluid sample, such as blood, that may thenbe collected by the sensor. In at least some embodiments, the fluidsample may be collected without moving the integrated sample acquisitionand analyte measurement device.

Various embodiments of methods of making sensors, according to thisdisclosure, include providing a sample chamber and/or measurement zonehaving an electrode surface area that, when filled with a sample to betested, provides a clinically accurate analyte level reading, withoutthe user having to enter a calibration code or the like that correspondsto the sensor, into a meter that is used to read the sensor. In certainembodiments, the sample chamber and/or measurement zone volume may bemodified, e.g., physically altered, during the manufacturing process ofthe sensor so that the resulting sensor meets a pre-determinedcalibration code or standard. In many embodiments, the physical alteringof the sensor is the last step of the manufacturing process. In othermethods, the area of the electrode(s) present in the sample chamberand/or measurement zone may be modified, e.g., physically altered,during the manufacturing process of the sensor so that the resultingsensor meets a pre-determined calibration code. In yet another method,prior to assembling the sensor, individual components or materials ofthe sensor could be tested; upon assembling of the sensors, the physicalcharacteristics of the sensor may be modified as needed to compensatefor the previously tested component variations to meet a pre-determinedcalibration code. Multiple calibration-adjusted sensors may beintermingled, without the need to record a calibration code, as all thesensors would have been physically altered to obtain the samecalibration.

In some embodiments, at least one pre-sensor or test sensor is made andtested for its slope and y-intercept. Subsequent sensors would beadjusted accordingly to have the desired, pre-determined slope andy-intercept; the adjustment would be based on the slope and y-interceptfrom the pre-sensor or test sensor. In some embodiments, a number oftest sensors (e.g., 10 or 100) may be made, their slope and y-interceptaveraged, and that average is used to adjust the shape and/or size of abatch of sensors (e.g., 1,000 sensors, 50,000 sensors, or 1,000,000sensors).

In certain embodiments, one particular method of forming a sensor, asdescribed above, includes forming at least one working electrode on afirst substrate and forming at least one counter or counter/referenceelectrode on a second substrate. A spacer layer is disposed on eitherthe first or second substrates. The spacer layer defines a chamber intowhich a sample may be drawn and held when the sensor is completed.Chemistry for detecting one or more analytes may be present on the firstor second substrate in a region that will be exposed within the samplechamber when the sensor is completed. The first and second substratesmay then be brought together and spaced apart by the spacer layer withthe sample chamber providing access to the at least one workingelectrode and the at least one counter or counter/reference electrode.The volume of the sample chamber, and optionally the volume of themeasurement zone, may be adjusted so that the resulting sensor meetscertain criteria.

Certain other embodiments include forming at least one working electrodeon a first substrate and forming at least one counter orcounter/reference electrode on the same, first substrate. One or twoadditional layers may be added to define a chamber into which a samplemay be drawn and held when the sensor is completed. Chemistry may bepresent in a region that will be exposed within the sample chamber whenthe sensor is completed. The substrates may then be brought together,forming a sample chamber providing access to the at least one workingelectrode and the at least one counter or counter/reference electrode.In some embodiments, the volume of the sample chamber, and optionallythe volume of the measurement zone, may be adjusted so that theresulting sensor meets certain criteria. Adjusting the volume of thesample chamber may or may not modify the electrode area. Additionally oralternately, in some embodiments, the surface area of the at least oneworking electrode and/or the at least one counter or counter/referenceelectrode are adjusted so that the resulting sensor meets certaincriteria. Adjusting the electrode area may or may not modify the volumeof the sample chamber.

These and various other features which characterize the invention arepointed out with particularity in the attached claims. For a betterunderstanding of the invention, its advantages, and objectives obtainedby its use, reference should be made to the drawings and to theaccompanying description, in which there is illustrated and describedpreferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, wherein like reference numerals andletters indicate corresponding structure throughout the several views:

FIG. 1 is a schematic view of a first embodiment of a sensor strip inaccordance with the present invention;

FIG. 2 is an exploded view of the sensor strip shown in FIG. 1, thelayers illustrated individually with the electrodes in a firstconfiguration;

FIG. 3 is an enlarged top plan view of a portion of the sensor strip ofFIG. 1;

FIG. 4 is an enlarged top plan view of an alternate embodiment of asensor strip, similar to FIG. 3;

FIG. 5 is a schematic view of a third embodiment of a sensor strip inaccordance with the present invention; and

FIG. 6 is an exploded view of the sensor strip shown in FIG. 5, thelayers illustrated individually with the electrodes in a firstconfiguration.

DETAILED DESCRIPTION

In some currently available systems, a value indicative of thecalibration code of a sensor is manually entered into the meter or otherequipment, for example, by the user. Based on the calibration code, themeter uses one of several programs or parameters stored within themeter. In other currently available systems, the sensor calibration codeis directly read by the meter or other equipment, thus not requiringinput or other interaction by the user. These sensors, however, stillhave a calibration code associated with them, which includes slope andy-intercept values. The slope and y-intercept values are used todetermine the analyte concentration based on the measured signal. Thecalibration code, whether inputted manually or automatically, is neededto standardize the analysis results received from non-standardizedsensors. In other words, different sensors vary, e.g., from lot to lot,a sufficient amount that, if no compensation were made, the resultswould differ from sensor to sensor and the results could be clinicallyinaccurate.

The sensors of this disclosure are calibration-adjusted to apre-determined calibration (slope and y-intercept), during themanufacturing process, to avoid the need for the user to input orotherwise set a calibration code for the sensor or perform othercalibration procedure(s) before using the sensor. The sensors of thisdisclosure are also calibration-adjusted to avoid the need for the meterto read a calibration code.

It has been determined that the measured signal (e.g., charge due toelectrooxidation or electroreduction) from the analyte in a sample isproportional to a physical element of the sensor. For example, whencoulometry is used to obtain a signal proportionate to the analyteconcentration, the signal obtained is proportional to the volume ofsample being assayed. For amperometry or other kinematical electrolysis,the signal is proportion to the area of the electrode(s), e.g., the atleast one working electrode, in the sample chamber. By physicallyaltering the sensor's sample chamber volume or electrode area within thesample chamber during the manufacturing process, e.g., after theassembly of multiple layers, the slope and y-intercept of the sensor lotcan be controlled, e.g., shifted, to provide a sensor with apre-determined calibration. In some embodiments, the relationshipbetween the sample chamber volume and the measured signal is linear.Additionally or alternatively, in some embodiments the relationshipbetween the electrode area and the measured signal is linear.

This disclosure also provides methods for making sensors that avoid theneed for the user to input or otherwise set a calibration code for thesensor, or perform other calibration procedure(s) before using thesensor.

Referring to the Drawings in general and FIGS. 1 and 2 in particular, afirst embodiment of a sensor 10 is schematically illustrated, hereinshown in the shape of a strip. It is to be understood that the sensormay be any suitable shape. Sensor strip 10 has a first substrate 12, asecond substrate 14, and a spacer 15 positioned therebetween. Sensorstrip 10 includes at least one working electrode 22 and at least onecounter electrode 24. Sensor strip 10 also includes an optionalinsertion monitor 30.

Sensor strip 10 has a first, distal end 10A and an opposite, proximalend 10B. At distal end 10A, sample to be analyzed is applied to sensor10. Distal end 10A could be referred as ‘the fill end’, ‘samplereceiving end’, or similar. Proximal end 10B of sensor 10 is configuredfor operable, and usually releasable, connecting to a device such as ameter.

Sensor strip 10 is a layered construction, in certain embodiments havinga generally rectangular shape, i.e., its length is longer than itswidth, although other shapes are possible as well, as noted above. Thelength of sensor strip 10 is from end 10A to end 10B.

The dimensions of a sensor may vary. In certain embodiments, the overalllength of sensor strip 10 may be no less than about 10 mm and no greaterthan about 50 mm. For example, the length may be between about 30 and 45mm; e.g., about 30 to 40 mm. It is understood, however that shorter andlonger sensor strips 10 could be made. In certain embodiments, theoverall width of sensor strip 10 may be no less than about 3 mm and nogreater than about 15 mm. For example, the width may be between about 4and 10 mm, about 5 to 8 mm, or about 5 to 6 mm. In one particularexample, sensor strip 10 has a length of about 32 mm and a width ofabout 6 mm. In another particular example, sensor strip 10 has a lengthof about 40 mm and a width of about 5 mm. In yet another particularexample, sensor strip 10 has a length of about 34 mm and a width ofabout 5 mm.

Briefly referring to FIGS. 3 and 4, two different configurations of aportion of sensors are illustrated. FIG. 3 shows a portion of sensorstrip 10 that includes first end 10A and sample chamber 20. FIG. 4 showsa portion of a sensor strip 10′ that includes a sensor first end 10A′and a sample chamber 20′. The shape of sensors 10, 10′ is the result ofphysically altering the sensor's measurement zone during themanufacturing process to provide sensor strips 10, 10′ withpredetermined calibration. Additional details are provided below.

Substrates and Spacer

As provided above, sensor strip 10 has first and second substrates 12,14, non-conducting, inert substrates which form the overall shape andsize of sensor strip 10. Substrates 12, 14 may be substantially rigid orsubstantially flexible. In certain embodiments, substrates 12, 14 areflexible or deformable. Examples of suitable materials for substrates12, 14 include, but are not limited, to polyester, polyethylene,polycarbonate, polypropylene, nylon, and other “plastics” or polymers.In certain embodiments the substrate material is “Melinex” polyester.Other non-conducting materials may also be used.

Substrate 12 includes first or distal end 12A and second or proximal end12B, and substrate 14 includes first or distal end 14A and second orproximal end 14B.

As indicated above, positioned between substrate 12 and substrate 14 maybe spacer 15 to separate first substrate 12 from second substrate 14. Insome embodiments, spacer 15 extends from end 10A to end 10B of sensorstrip 10, or extends short of one or both ends. Spacer 15 is an inertnon-conducting substrate, typically at least as flexible and deformable(or as rigid) as substrates 12, 14. In certain embodiments, spacer 15 isan adhesive layer or double-sided adhesive tape or film that iscontinuous and contiguous. Any adhesive selected for spacer 15 should beselected to not diffuse or release material which may interfere withaccurate analyte measurement.

In certain embodiments, the thickness of spacer 15 may be constantthroughout, and may be at least about 0.01 mm (10 μm) and no greaterthan about 1 mm or about 0.5 mm. For example, the thickness may bebetween about 0.02 mm (20 μm) and about 0.2 mm (200 μm). In one certainembodiment, the thickness is about 0.05 mm (50 μm), and about 0.1 mm(100 μm) in another embodiment.

Sample Chamber

The sensor includes a sample chamber for receiving a volume of sample tobe analyzed; in the embodiment illustrated, particularly in FIG. 1,sensor strip 10 includes sample chamber 20 having an inlet 21 for accessto sample chamber 20. In the embodiment illustrated, sensor strip 10 isa side-fill sensor strip, having inlet 21 present on a side edge ofstrip 10. Tip-fill sensors, having an inlet at, for example, end 10A,are also within the scope of this disclosure, as well as corner and topfilling sensors.

Sample chamber 20 is configured so that when a sample is provided inchamber 20, the sample is in electrolytic contact with both a workingelectrode and a counter electrode, which allows electrical current toflow between the electrodes to effect the electrolysis (electrooxidationor electroreduction) of the analyte.

Sample chamber 20 is defined by substrate 12, substrate 14 and spacer15; in many embodiments, sample chamber 20 exists between substrate 12and substrate 14 where spacer 15 is not present. Typically, a portion ofspacer 15 is removed to provide a volume between substrates 12, 14without spacer 15; this volume of removed spacer is sample chamber 20.For embodiments that include spacer 15 between substrates 12, 14, thethickness of sample chamber 20 is generally the thickness of spacer 15.

Sample chamber 20 has a volume sufficient to receive a sample ofbiological fluid therein. In some embodiments, such as when sensor strip10 is a small volume sensor, sample chamber 20 has a volume that istypically no more than about 1 μL, for example no more than about 0.5μL, and also for example, no more than about 0.25 μL. A volume of nomore than about 0.1 μL is also suitable for sample chamber 20, as arevolumes of no more than about 0.05 μL and about 0.03 μL.

A measurement zone is contained within sample chamber 20 and is theregion of the sample chamber that contains only that portion of thesample that is interrogated during the analyte assay. In some designs,the measurement zone has a volume that is approximately equal to thevolume of sample chamber 20. In some embodiments the measurement zoneincludes 80% of the sample chamber, 90% in other embodiments, and about100% in yet other embodiments.

As provided above, the thickness of sample chamber 20 correspondstypically to the thickness of spacer 15. Particularly for facingelectrode configurations, as in the sensor illustrated in FIG. 2, thisthickness is small to promote rapid electrolysis of the analyte, as moreof the sample will be in contact with the electrode surface for a givensample volume. In addition, a thin sample chamber 20 helps to reduceerrors from diffusion of analyte into the measurement zone from otherportions of the sample chamber during the analyte assay, becausediffusion time is long relative to the measurement time, which may beabout 5 seconds or less.

Electrodes

As provided above, the sensor includes a working electrode and at leastone counter electrode. The counter electrode may be a counter/referenceelectrode. If multiple counter electrodes are present, one of thecounter electrodes will be a counter electrode and one or more may bereference electrodes.

For sensor 10, at least one working electrode is positioned on one offirst substrate 12 and second substrate 14 in the measurement zoneand/or sample chamber. In FIG. 2, working electrode 22 is illustrated onsubstrate 12. Working electrode 22 extends from the sample chamber 20,proximate distal end 10A, to the other end of the sensor 10, end 10B, asan electrode extension called a “trace”. The trace provides a contactpad 23 for providing electrical connection to a meter or other device toallow for data and measurement collection, as will be described later.Contact pad 23 may be positioned on a tab 26 that extends from thesubstrate on which working electrode 22 is positioned, such as substrate12. In some embodiments, a tab has more than one contact pad positionedthereon. In alternate embodiments, a single contact pad is used toprovide a connection to one or more electrodes; that is, multipleelectrodes are coupled together and are connected via one contact pad.

Working electrode 22 may be a layer of conductive material such as gold,carbon, platinum, ruthenium dioxide, palladium, or other non-corroding,conducting material. Working electrode 22 may be a combination of two ormore conductive materials. An example of a suitable conductive epoxy isECCOCOAT CT5079-3 Carbon-Filled Conductive Epoxy Coating (available fromW.R. Grace Company, Woburn, Mass.). The material of working electrode 22typically has relatively low electrical resistance and is typicallyelectrochemically inert over the potential range of the sensor duringoperation.

Working electrode 22 may be applied on substrate 12 by any of variousmethods, including by being deposited, such as by vapor deposition orvacuum deposition or otherwise sputtered, printed on a flat surface orin an embossed or otherwise recessed surface, transferred from aseparate carrier or liner, etched, or molded. Suitable methods ofprinting include screen-printing, piezoelectric printing, ink jetprinting, laser printing, photolithography, and painting.

As provided above, at least a portion of working electrode 22 isprovided in sample chamber 20 for the analysis of analyte, inconjunction with the counter electrode.

The sensor includes at least one counter electrode positioned within themeasurement zone and/or sample chamber. In FIG. 2, counter electrode 24is illustrated on substrate 14. In alternate embodiments, a counterelectrode is present on a different 10 surface or substrate, such assubstrate 12. Counter electrode 24 extends from the sample chamber 20,proximate first end 10A, to the other end of the sensor 10, end 10B, asan electrode extension called a “trace”. The trace provides a contactpad 25 for providing electrical connection to a meter or other device toallow for data and measurement collection, as will be described later.Contact pad 25 may be positioned on a tab 27 that extends from thesubstrate on which counter electrode 24 is positioned, such as substrate12 or 14. In some embodiments, a tab has more than one contact padpositioned thereon. In alternate embodiments, a single contact pad isused to provide a connection to one or more electrodes; that is,multiple electrodes are coupled together and are connected via onecontact pad.

Counter electrode 24 may be constructed in a manner similar to workingelectrode 22. Suitable materials for the counter/reference or referenceelectrode include Ag/AgCl or Ag/AgBr on a non-conducting base materialor silver chloride on a silver metal base. The same materials andmethods may be used for counter electrode 24 as are available forworking electrode 22, although different materials and methods may alsobe used. Counter electrode 24 may include a mix of multiple conductingmaterials, such as Ag/AgCl and carbon.

Working electrode 22 and counter electrode 24 may be disposed oppositeto and facing each other to form facing electrodes. See for example,FIG. 2, which has working electrode 22 on substrate 12 and counterelectrode 24 on substrate 14, forming facing electrodes. In thisconfiguration, the sample chamber is typically present between the twoelectrodes 22, 24. Working electrode 22 and counter electrode 24 mayalternately be positioned generally planar to one another, such as onthe same substrate, to form co-planar or planar electrodes.

In some instances, it is desirable to be able to determine when thesample chamber of the sensor is sufficiently filled with sample. Sensorstrip 10 may be indicated as filled, or substantially filled, byobserving a signal between an optional indicator electrode and one orboth of working electrode 22 or counter electrode 24 as sample chamber20 fills with fluid. When fluid reaches the indicator electrode, thesignal from that electrode will change. Suitable signals for observinginclude, for example, voltage, current, resistance, impedance, orcapacitance between the indicator electrode and, for example, workingelectrode 22. Alternatively, the sensor may be observed after filling todetermine if a value of the signal (e.g., voltage, current, resistance,impedance, or capacitance) has been reached indicating that the samplechamber is filled.

Typically, the indicator electrode is further downstream from a sampleinlet, such as inlet 21, than working electrode 22 and/or counterelectrode 24.

For side-fill sensors, such as sensor 10 of FIGS. 1 and 2, an indicatorelectrode may be present on each side of the counter electrode. Thispermits the user to fill the sample chamber from either the left orright side with an indicator electrode disposed further upstream. Thisthree-electrode configuration is not necessary. Side-fill sensors mayalso have a single indicator electrode and may include some indicationas to which side should be placed in contact with the sample fluid.

The indicator electrode may also be used to improve the precision of theanalyte measurements. The indicator electrode may operate as a workingelectrode or as a counter electrode or counter/reference electrode.Measurements from the indicator electrode/working electrode may becombined (e.g., added or averaged) with those from the firstcounter/reference electrode/working electrode to obtain more accuratemeasurements.

The sensor or equipment that the sensor connected is with (e.g., ameter) may include a signal (e.g., a visual sign or auditory tone) thatis activated in response to activation of the indicator electrode toalert the user that the desired zone has been filled. The sensor orequipment may be configured to initiate a reading when the indicatorelectrode indicates that the measurement zone has been filled with orwithout alerting the user. The reading may be initiated, for example, byapplying a potential between the working electrode and the counterelectrode and beginning to monitor the signals generated at the workingelectrode.

Sensing Chemistry

In addition to working electrode 22, sensing chemistry material(s) arepreferably provided in sample chamber 20 for the analysis of theanalyte. Sensing chemistry material facilitates the transfer ofelectrons between working electrode 22 and the analyte in the sample.Any sensing chemistry may be used in sensor strip 10; the sensingchemistry may include one or more materials.

The sensing chemistry may be diffusible or leachable, or non-diffusibleor non-leachable. For purposes of discussion herein, the term“diffusible” will be used to represent “diffusible or leachable” and theterm “non-diffusible” will be used to represent “non-diffusible ornon-leachable” and variations thereof. Placement of sensing chemistrycomponents may depend on whether they are diffusible or not. Forexample, both non-diffusible and/or diffusible component(s) may form asensing layer on working electrode 22. Alternatively, one or morediffusible components may be present on any surface in sample chamber 20prior to the introduction of the sample to be analyzed. As anotherexample, one or more diffusible component(s) may be placed in the sampleprior to introduction of the sample into sample chamber 20.

The sensing chemistry generally includes an electron transfer agent thatfacilitates the transfer of electrons to or from the analyte. Theelectron transfer agent may be diffusible or non-diffusible, and may bepresent on working electrode 22 as a layer. One example of a suitableelectron transfer agent is an enzyme which catalyzes a reaction of theanalyte. For example, a glucose oxidase or glucose dehydrogenase, suchas pyrroloquinoline quinone glucose dehydrogenase (PQQ), is used whenthe analyte is glucose. Other enzymes may be used for other analytes.

The electron transfer agent, whether it is diffusible or not,facilitates a current between working electrode 22 and the analyte andenables the electrochemical analysis of molecules. The agent facilitatesthe transfer electrons between the electrode and the analyte.

This sensing chemistry may, additionally to or alternatively to theelectron transfer agent, include a redox mediator. Certain embodimentsuse a redox mediator that is a transition metal compound or complex.Examples of suitable transition metal compounds or complexes includeosmium, ruthenium, iron, and cobalt compounds or complexes. In thesecomplexes, the transition metal is coordinatively bound to one or moreligands, which are typically mono-, di-, tri-, or tetradentate. Theredox mediator may be a polymeric redox mediator or a redox polymer(i.e., a polymer having one or more redox species). Examples of suitableredox mediators and redox polymers are disclosed in U.S. Pat. No.6,338,790, for example, and in U.S. Pat. Nos. 6,605,200 and 6,605,201.

If the redox mediator is non-diffusible, then the redox mediator may bepresent on working electrode 22 as a layer. In an embodiment having aredox mediator and an electron transfer agent, if the redox mediator andelectron transfer agent are both non-leachable, then both components areon working electrode 22 as individual layers, or combined and applied asa single layer.

The redox mediator, whether diffusible or not, mediates a currentbetween working electrode 22 and the analyte and enables theelectrochemical analysis of molecules which may not be suited for directelectrochemical reaction on an electrode. The mediator functions as anagent to transfer electrons between the electrode and the analyte.

Insertion Monitor

The sensor may include an indicator to notify when proper insertion ofthe sensor into receiving equipment, such as a meter, has occurred. Asseen in FIGS. 1 and 2, sensor strip 10 includes insertion monitor 30 onan exterior surface of one of substrates 12, 14, in the illustratedsensor, sensor 10. Insertion monitor 30 is configured and arranged toclose an electrical circuit when sensor 10 is properly inserted into themeter connector.

Insertion monitor 30 may be a stripe extending across an exteriorsurface of sensor 10, for example, from side edge to side edge, with onecontact pad for connection to a meter. It is understood that inalternate embodiments of the insertion monitor, the stripe need notextend to both side edges. In other embodiments, the insertion monitormay be two or more contact pads for connection to a meter. The two ormore contact pads could electrically connected to each other by amaterial, such as a conductive ink.

Insertion monitor 30 can be used to encode information regarding sensorstrip 10. The encoded information may be, for example, the test timeneeded for accurate analyte concentration analysis, the expiration dateof sensor strip 10, various correction factors, such as forenvironmental temperature and/or pressure, selection of the analyte tobe analyzed (e.g., glucose, ketone, lactate), and the like.Additionally, insertion monitor 30 can be used to encode calibrationinformation for the sensor, e.g., for the manufacturing lot or thatspecific sensor strip. However, in accordance with this disclosure, thesensor requires no calibration code; rather, the sensor is configuredwith a pre-determined calibration, based on the volume of themeasurement zone.

Additional details regarding insertion monitors, and their use forencoding information, are described, for example, in U.S. Patentapplication publication no. 2006/0091006 A1. Additionally, U.S. Patentapplication publication no. 2006/0091006 A1 provides various detailsregarding connection of sensors with insertion monitors with meters andconnectors.

Referring to FIGS. 5 and 6 in particular, an alternate embodiment of asensor is illustrated as sensor strip 110. Similar to sensor strip 110,sensor strip 110 has a first substrate 112, a second substrate 114, anda spacer 115 positioned therebetween. Sensor strip 110 includes at leastone working electrode 122 and at least one counter electrode 124.

Sensor strip 110 has a first, distal end 110A and an opposite, proximalend 110B. At distal end 110A, sample to be analyzed is applied to sensor110. Distal end 110A could be referred as ‘the fill end’, ‘samplereceiving end’, or similar. Proximal end 110B of sensor 110 isconfigured for operable, and preferably releasable, connecting to adevice such as a meter. Similar to sensor strip 10, sensor strip 110 isa layered construction, in certain embodiments having a generallyrectangular shape, which is formed by first and second substrates 112,114. Substrate 112 includes first or distal end 112A and second orproximal end 112B, and substrate 114 includes first or distal end 114Aand second or proximal end 114B. The discussion above about substrates12, 14 and spacer 15 applies to substrates 112, 114 and spacer 15.

Sensor strip 110 includes sample chamber 120 having an inlet 121 foraccess to sample chamber 120. Sensor strip 110 is a tip-fill sensor,having inlet 121 at end 110A.

Similar to sample chamber 20 of sensor strip 10, sample chamber 120 isdefined by substrate 112, substrate 114 and spacer 115. Generallyopposite to inlet 121, through substrate 112 is a vent 130 from samplechamber 120. The discussion above about sample chamber 20 and itsmeasurement zone applies to sample chamber 120.

For sensor 110, at least one working electrode 122 is illustrated onsubstrate 114. Working electrode 122 extends from end 114A into samplechamber 120 to end 114B and 110B. Sensor 110 also includes at least onecounter electrode 124, in this embodiment on substrate 114. Counterelectrode 124 extends from sample chamber 120, proximate first end 110A,to end 110B, as an electrode extension called a “trace”. Workingelectrode 122 and counter electrode 124 are present on the samesubstrate e.g., as planar or co-planar electrodes. The electrodes 122,124 may include sensing chemistry material(s) thereon.

General Method for Manufacturing Sensors

Sensor strips 10, 110 discussed above, are sandwiched or layeredconstructions having substrates 12, 14, 112, 114 spaced apart, such asby spacer 15, 115. Such a construction may be made by laminating thevarious layers together, in any suitable manner. An alternate method formaking sensor strips 10, 110, and other sensors in accordance with theinvention, is to mold the sensors.

Molding may include positioning at least two spaced apart electricallyconductive electrodes (e.g., wires) in a mold, and molding a body ofinsulative material around the electrodes, with one end having thereinmeans for receiving a fluid sample. More specifically, molding couldinclude positioning at least two spaced apart electrically conductiveelectrodes (e.g., wires) in a mold, before or after molding, treating atleast one of the electrodes with one or more chemicals to change theelectrical properties of the treated electrode upon contact with a fluidsample, and molding a body of insulative material around the electrodeswith one end having therein means for receiving a fluid sample. The bodymay be molded in multiple pieces, e.g., two pieces, with a body and endcap for attaching to one another after the molding is completed, or in asingle piece.

A sensor may be made by positioning electrodes on one or moresubstrates, the substrates including a first substrate, optionallycontacting at least a portion of at least one electrode with sensingmaterial(s), and configuring the sensor by positioning a spacer betweenthe two substrates to maintain the substrates in a fixed, layeredorientation relative to each other.

Calibration of Sensors

Whether the sensors are laminated, molded, or made by some otherprocess, after or during forming the sensor, a portion of the sensor isphysically modified (e.g., removed, re-shaped, reacted, etc.) to providethe sensor with a pre-determined slope and y-intercept. Typically, thephysically modified portion of the sensor includes the sample chamberand/or measurement zone. In accordance with some embodiments of thisdisclosure, the sample chamber shape and/or size is altered to providethe sensor with the desired pre-determined slope and y-intercept. Inmany embodiments, the shape and/or size of the sample chamber and/ormeasurement zone is physically modified. Additionally or alternately, inaccordance with some embodiments of this disclosure, the electrode areawithin the sample chamber and/or measurement zone is altered, sometimeswithout altering the sample chamber shape and/or size. In manyembodiments, the electrode area is physically modified.

Referring again to FIGS. 3 and 4, two different configurations ofsensors are illustrated. FIG. 3 shows a portion of sensor strip 10 thatincludes first end 10A and FIG. 4 shows a portion of a sensor strip 10′that includes a sensor first end 10A′. Sensor strip 10 includes firstedge 102 (which in this embodiment is also sensor end 10A), second edge104 and third edge 106, each of which is a straight, linear edge. Thecorners formed by the meeting of edges 104, 106 with edge 102 areangular, in this embodiment, having an internal angle of about 108degrees. In this embodiment, sample chamber 20 extends across sensorstrip 10 from edge 104 to edge 106. Sensor strip 10′ includes first edge102′ (which in this embodiment is also sensor end 10A′), second edge104′ and third edge 106′. Edges 104′ and 106′ are arcuate edges.Additionally, the corners formed by the meeting of edges 104′, 106′ withedge 102′ are rounded or radiused. Also in this embodiment, samplechamber 20′ extends across sensor 10′ from edge 104′ to edge 106′. Thevolume of sample chamber 20, 20′ is defined by side edges 104, 104′ and106, 106′ and the thickness of the sample chamber.

To clarify understanding, the following discussion will use the term“pre-sensor” when referring to the sensor prior to any physicalalteration of the sensor.

Sensors 10, 10′ are the result of physically altering the sample chamberand/or measurement zone after the manufacturing process of thepre-sensor to provide sensors that have a pre-determined slope andy-intercept. In some embodiments, “physically altering” includesremoving a portion of the sample chamber and/or measurement zone of thepre-sensor. FIG. 3 illustrates a first phantom portion 104 ^(o) (i.e.,104 superscript naught), which corresponds to the portion of thepre-sensor removed to form edge 104, and a second phantom portion 106^(o) (i.e., 106 superscript naught), which corresponds to the portion ofthe pre-sensor removed to form edge 106. By removing phantom portions104 ^(o), 106 ^(o), a portion of the sample chamber, i.e., that presentin portions 104 ^(o), 106 ^(o), is also removed, thus physicallyaltering the pre-sensor. For sensors 10, 10′ of FIGS. 3 and 4, thecalibration code is proportional to the volume of the measurement zoneand/or the sample chamber of the sensor.

Referring to FIG. 5, sensor 110 is the result of physically altering theelectrode area and the sample chamber and/or measurement zone after themanufacturing process of the pre-sensor to provide sensors that have apre-determined slope and y-intercept. FIG. 5 illustrates phantom portion110 ^(o) (i.e., 110 superscript naught), which corresponds to theportion of the pre-sensor removed to form edge 110A. By removing phantomportion 110 ^(o), a portion of the working electrode 122, i.e., thatpresent on substrate 114 within phantom portion 110 ^(o), is alsoremoved, thus physically altering the pre-sensor. For sensor 110 above,the calibration slope and y-intercept are proportional to the area ofthe electrode(s), e.g., working electrode 122, in the sample chamber ofthe sensor. In this embodiment, the volume of the sample chamber isreduced, due to the removal of phantom portion 110 ^(o). It is notedthat in alternate embodiments, the sample chamber volume and/ormeasurement zone volume may remain the same although the area of theelectrodes is modified. One exemplary method for modifying the electrodearea, e.g., removing area, is by the use of non-invasive procedures,such as a single or multiple energy beams (e.g., lasers, UV light,electron beam, etc.) that pass through the inert substrates butphysically alter the electrodes. In this process, areas of electrode(s)may be removed or otherwise rendered inactive.

To provide a plurality of sensors, such as sensor strips 10, 10′, 110with the same pre-determined calibration from a plurality ofpre-sensors, each of the pre-sensors may be physically altered, asneeded, to obtain the desired pre-determined physical characteristicsand the desired sensor. It is understood that this discussion alsoapplies to a batch or lot of sensors in addition to a single sensor. Forexample, a first pre-sensor may have a response that is too highcompared to the desired level and a second pre-sensor may have aresponse that is within the desired level. In such a situation, aportion of the first pre-sensor may be removed to provide a sensorhaving a measurement zone, sample chamber, or electrode area that iscomparable to that of the second pre-sensor and is within the desiredlevel.

In some situations, however, a pre-sensor, e.g., a third sensor strip,may have a response that is too low compared to the desired level.Because in most embodiments it would be difficult or impractical toincrease the measurement zone, sample chamber, and/or electrode area ofthe pre-sensor after it has been assembled, in some manufacturingoperations the desired response level may be artificially lowered inorder to pre-calibrate the sensor. With such an artificially lowereddesired level, for a pre-sensor that has a response within that desiredartificially low level, a pre-determined portion of the pre-sensor'sactive area may be removed to obtain a sensor with the actual desiredlevel; for a pre-sensor that has a response above the desiredartificially low, a larger portion than the pre-determined portion ofthe pre-sensor's active area may be removed to obtain a sensor with theactual desired level; and for a pre-sensor that has a response below thedesired artificially low level, a smaller portion than thepre-determined portion of the pre-sensor's active area is removed inorder to obtain a sensor with the actual desired level. In other words,using such a methodology, all the pre-sensors would be physicallyaltered to obtain sensors with the same desired pre-determinedcalibration.

The pre-sensor is modified in order to obtain the desired pre-determinedcalibration, either by altering the volume of the sample chamber and/ormeasurement zone or by the electrode area in the sample chamber.Referring to FIGS. 3 and 4, in this embodiment, the volume of the samplechamber and/or measurement zone is modified by removing phantom portions104 ^(o), 106 ^(o), and the electrode area is modified in FIG. 5 byremoving phantom portion 110 ^(o).

In some embodiments, there may be no actual pre-sensor that issubsequently modified to form the sensor, but rather, a pre-sensor isused as a template for one or more sensors (e.g., batch or lot ofsensors, e.g., at least 100 sensors, at least 1,000 sensors, or even atleast 50,000 sensors). For example, multiple sensors may be obtainedfrom, e.g., a large sheet construction having working electrodes,counter electrodes and sample chambers. See for example, U.S. Pat. No.6,338,790, particularly FIGS. 31A and 31B and the description associatedtherewith, which describes methods of making a plurality of sensors froma large sandwiched sheet construction. From this sheet, one (or more)test sensors could be removed (e.g., punched) using a standard template(e.g., shape and size), and these test sensors could be tested for theirdifference from the desired slope and y-intercept, and the resultstypically averaged. Subsequently removed sensors would be modified fromthe test sensor, as needed, by removing (e.g., punching) anappropriately shaped and sized sensor, which may differ from the testsensors, to obtain the desired slope and y-intercept. In this method,the test sensors provide a guide for the modification needed, so thateach sensor is not individually tested.

It is understood that other configurations of phantom portions would besuitable. For example, sensor 10 of FIG. 3 has edge 102 and edges 104,106 forming an angle of about 108 degrees. This corner angle could beabout 90 degrees or be a high as 180 degrees; in most embodiments,however, this corner angle is in the range of about 90 to about 145degrees. Angles less than 90 degrees could be used for a concave edge102, 102′. The corners could be sharp, as in FIG. 3, or rounded, as inFIG. 4. Any or all of edges 102, 104, 106 may be straight or curved,with concave, convex, or a combination of shapes. Both sensor strips 10,10′ have edge 102, 102′ forming end 10A, 10A′; in alternate embodiments,the sensor end could be defined by the meeting of edges 104, 106 (i.e.,the side edges meet at a point with no end edge). In some embodiments,the sensor could be asymmetrical, e.g., having only one portion removedfrom the sensor. Other shapes for sensors would be suitable. FIGS. 5 and6 illustrate sensor strip 110 with a blunt end 110A, having 90 degreecorners. After providing any of sensors 10, 10′, 110, the proximal ends,e.g., 10B, 110B could be adjusted so that all sensors in the lot havethe same final size.

Application of the Sensor

A common use for a sensor of the present invention, such as sensor strip10, 10′ 110, is for the determination of analyte concentration in abiological fluid, such as glucose concentration in blood, interstitialfluid, and the like, in a patient or other user. Additional analytesthat may be determined include but are not limited to, for example,acetyl choline, amylase, bilirubin, cholesterol, chorionic gonadotropin,creatine kinase (e.g., CK-MB), creatine, DNA, fructosamine, glucose,glutamine, growth hormones, hormones, ketones, lactate, peroxide,prostate-specific antigen, prothrombin, RNA, thyroid stimulatinghormone, and troponin. The concentration of drugs, such as, for example,antibiotics (e.g., gentamicin, vancomycin, and the like), digitoxin,digoxin, drugs of abuse, theophylline, and warfarin, may also bedetermined.

Sensors may be available at pharmacies, hospitals, clinics, fromdoctors, and other sources of medical devices. Multiple sensors may bepackaged together and sold as a single unit; e.g., a package of about25, about 50, or about 100 sensors, or any other suitable number. A kitmay include one or more sensors, and additional components such ascontrol solutions and/or lancing device and/or meter, etc.

Sensors may be used for an electrochemical assay, or, for a photometrictest. Sensors are generally configured for use with an electrical meter,which may be connectable to various electronics. A meter may beavailable at generally the same locations as the sensors, and sometimesmay be packaged together with the sensors, e.g., as a kit.

Examples of suitable electronics connectable to the meter include a dataprocessing terminal, such as a personal computer (PC), a portablecomputer such as a laptop or a handheld device (e.g., personal digitalassistants (PDAs)), and the like. The electronics are configured fordata communication with the receiver via a wired or a wirelessconnection. Additionally, the electronics may further be connected to adata network (not shown) for storing, retrieving and updating datacorresponding to the detected glucose level of the user.

The various devices connected to the meter may wirelessly communicatewith a server device, e.g., using a common standard such as 802.11 orBluetooth RF protocol, or an IrDA infrared protocol. The server devicecould be another portable device, such as a Personal Digital Assistant(PDA) or notebook computer, or a larger device such as a desktopcomputer, appliance, etc. In some embodiments, the server device has adisplay, such as a liquid crystal display (LCD), as well as an inputdevice, such as buttons, a keyboard, mouse or touch-screen. With such anarrangement, the user can control the meter indirectly by interactingwith the user interface(s) of the server device, which in turn interactswith the meter across a wireless link.

The server device may also communicate with another device, such as forsending data from the meter and/or the service device to a data storageor computer. For example, the service device could send and/or receiveinstructions (e.g., an insulin pump protocol) from a health careprovider computer. Examples of such communications include a PDAsynching data with a personal computer (PC), a mobile phonecommunicating over a cellular network with a computer at the other end,or a household appliance communicating with a computer system at aphysician's office.

A lancing device or other mechanism to obtain a sample of biologicalfluid, e.g., blood, from the patient or user may also be available atgenerally the same locations as the sensors and the meter, and sometimesmay be packaged together with the sensor and/or meter, e.g., as a kit.

The sensors are particularly suited for inclusion in an integrateddevice, i.e., a device which has the sensor and a second element, suchas a meter or a lancing device, in the device. The integrated device maybe based on providing an electrochemical assay or a photometric assay.In some embodiments, sensors may be integrated with both a meter and alancing device. Having multiple elements together in one device reducesthe number of devices needed to obtain an analyte level and facilitatesthe sampling process. For example, embodiments may include a housingthat includes one or more of the sensor strips, a skin piercing elementand a processor for determining the concentration of an analyte in asample applied to the strip. A plurality of sensors may be retained in acassette in the housing interior and, upon actuation by a user, a singlesensor may be dispensed from the cassette so that at least a portionextends out of the housing for use.

Operation of the Sensor Strip

In use, a sample of biological fluid is provided into the sample chamberof the sensor, where the level of analyte is determined. The analysismay be based on providing an electrochemical assay or a photometricassay. In many embodiments, it is the level of glucose in blood that isdetermined. Also in many embodiments, the source of the biological fluidis a drop of blood drawn from a patient, e.g., after piercing thepatient's skin with a lancing device, which could be present in anintegrated device, together with the sensor strip.

Prior to providing the sample to the sensor, or even after providing thesample to the sensor, there is no need for the user to input acalibration code or other information regarding the operation and/orinteraction of the sensor with the meter or other equipment. The sensoris configured so that the results received from the analysis areclinically accurate, without the user having to adjust the sensor or themeter. The sensor is physically configured to provide accurate resultsthat are repeatable by a batch of sensors.

After receipt of the sample in the sensor, the analyte in the sample is,e.g., electrooxidized or electroreduced, at the working electrode andthe level of current obtained at the counter electrode is correlated asanalyte concentration. The sensor may be operated with or withoutapplying a potential to the electrodes. In one embodiment, theelectrochemical reaction occurs spontaneously and a potential need notbe applied between the working electrode and the counter electrode. Inanother embodiment, a potential is applied between the working electrodeand the counter electrode.

The invention has been described with reference to various specific andpreferred embodiments and techniques. However, it will be apparent toone of ordinarily skill in the art that many variations andmodifications may be made while remaining within the spirit and scope ofthe invention. It is understood that elements or features present on oneembodiment described above could be used on other embodiments. Forexample, the discussion above has been directed to modifying the sensorbased on an output (e.g., charge) from an assembled sensor. In analternate embodiment, individual components or materials of the sensorcould be tested prior to assembling the sensor, and then modifying thesensor as needed to compensate for the previous test. For example, thesensing chemistry activity may be tested prior to incorporation of thechemistry in a sensor. If, for example, the activity is below thedesired standard, when incorporated into sensor, the sensors could bephysically adjusted (e.g., sample chamber volume or electrode areaincreased) to compensate for the low chemistry activity. Similarly, ifthe activity is above the desired standard, when incorporated intosensor, the sensors could be physically adjusted (e.g., sample chambervolume or electrode area decreased) to compensate for the high chemistryactivity.

Experimental

Five sensor strips, each having a distal end similar to that illustratedin FIG. 4, were punched from a laminated sheet composed of twosubstrates and a spacer layer therebetween, with at least one workingelectrode and at least one counter electrode in facing configuration.Each of the sensor strips had arcuate edges, similar to edges 104′, 106′in FIG. 4. The table below provides parameters for the five sensorstrips. The “tip distance” was the distance between the distal most endof the sensor strip (e.g., end 10A′ in FIG. 4) and the sample chamber(e.g., sample chamber 20′ in FIG. 4). The punch that formed the distalend and the arcuate edges was the same punch for each of the sensorstrips. Thus, as the distance between the tip and the sample chamberincreased, the length of the sample chamber (between the arcuate edges)increased, thus increasing the sample chamber volume.

Tip distance Sample chamber volume Charge (0.001 inch) (nanoliter)(microcoulombs) 10 97 98.7 20 103 107.7 30 109 115.9 40 114 123.4 50 120127.9

This data shows a linear relationship between the sample chamber volumeand the measured charge; the linear equation is y=1.3x−26.4. Also, thedata shows a linear relationship between the tip distance and themeasured charge; the linear equation is y=0−0.74x+92.5. With thisknowledge, the punch position to achieve the desired sensor response forthis batch of sensors can be calculated.

All patents and other references in this specification are indicative ofthe level of ordinary skill in the art to which this invention pertains.All patents and other references are herein incorporated by reference tothe same extent as if each individual patent or reference wasspecifically and individually incorporated by reference.

1-22. (canceled)
 23. A method of making a test sensor adapted to assistin determining the concentration of an analyte in a fluid sample, themethod comprising the acts of: providing a lid; providing a base;attaching the lid to the base to form an attached lid-base structure,the lid-base structure having a first end adapted to receive the fluidsample and a second opposing end adapted to be placed into a meter;assigning auto-calibration information to the lid-base structure; andforming the sensor such that the shape of the sensor corresponds to theauto-calibration information.
 24. The method of claim 23, wherein thetest sensor further includes a spacer, the spacer being located betweenthe lid and the base.
 25. The method of claim 23, wherein theauto-calibration information is a program auto-calibration number. 26.The method of claim 23, wherein the test sensor is an electrochemicaltest sensor.
 27. A method of making a test sensor adapted to assist indetermining the concentration of an analyte in a fluid sample, themethod comprising the acts of: providing a lid; providing a base;attaching the lid to the base to form an attached lid-base structure,the lid-base structure having a first end adapted to receive the fluidsample and a second opposing end adapted to be placed into a meter;assigning auto-calibration information to the lid-base structure; andforming at least one cutout on the sensor such that the shape,dimensions and/or number of the at least one cutout corresponds to theprogram auto-calibration number.
 28. The method of claim 27, wherein theat least one cutout is a plurality of cutouts.
 29. The method of claim27, wherein the test sensor further includes a spacer, the spacer beinglocated between the lid and the base.
 30. The method of claim 27,wherein the auto-calibration information is a program auto-calibrationnumber.
 31. A method of making a test sensor adapted to assist indetermining the concentration of an analyte in a fluid sample, themethod comprising the acts of: providing a lid; providing a base;attaching the lid to the base to form an attached lid-base structure,the lid-base structure having a first end adapted to receive the fluidsample and a second opposing end adapted to be placed into a meter;assigning auto-calibration information to the lid-base structure; andforming at least one partial cutout on the sensor such that the shape,dimensions and/or number of the at least one partial cutout correspondsto the program auto-calibration number.
 32. The method of claim 31,wherein the at least one partial cutout is exactly one partial cutout.33. The method of claim 31, wherein the test sensor further includes aspacer, the spacer being located between the lid and the base.
 34. Themethod of claim 31, wherein the auto-calibration information is aprogram auto-calibration number.